Origin of Species Variorum

daughters; at ichneumonidæ feeding within the living bodies of caterpillars; and at other such cases. The wonder indeed is, on the theory of natural selection, that more cases of the want of absolute perfection have not been observed.

The complex and little known laws governing acknowledged variations are the same, as far as we can see, with the laws which have governed the production of so-called specific differences. In both cases physical conditions seem to have produced some direct and definite effect, but how much we cannot say. Thus when varieties enter any new station, they occasionally assume some of the characters proper to the species of that station. In both varieties and species, use and disuse seem to have produced a considerable effect; for it is impossible to resist this .. conclusion when we look, for instance, at the logger-headed duck, which has wings incapable of flight, in nearly the same condition as in the domestic duck; or when we look at the burrowing tucutucu, which is occasionally blind, and then at certain moles, which are habitually blind and have their eyes covered with skin; or when we look at the blind animals inhabiting the dark caves of America and Europe. In varieties and species correlated variation seems to have played an important part, so that when one part has been modified other parts have been necessarily modified. In both varieties and species reversions to long-lost characters occur. How inexplicable on the theory of creation is the occasional appearance of stripes on the shoulders and legs of the several species of the horse-genus and of their hybrids! How simply is this fact explained if we believe that these species are all descended from a striped progenitor, in the same manner as the several domestic breeds of the pigeon are descended from the blue and barred rock-pigeon!